Corvettes, ships closely identified with Canada's wartime navy, were used to escort convoys bringing troops and supplies across the Atlantic. Convoys ran the constant risk of attack from Nazi U-boats (submarines). This film re-enacts a successful Corvette action against a U-boat. The narrative device of voicing the possible internal dialogue of crew members creates a sense of immediacy.

A film tribute to the Royal Canadian Navy. The stars: those men who sail the fighting ship Port Arthur, credited, shortly after the picture was completed, with sinking an Italian submarine in the Mediterranean. The film reaches a climax when a submarine is detected approaching the convoy and the signal for "action stations" is sounded throughout the ship.